Cultivation 



535 



colonies appear rounded, whitish, opaque, and prominent, 

 like drops of milk. This appearance of the colonies also 

 shows well if the cultures are kept for the first twelve to 

 sixteen hours at 37C., and afterward at the room temper- 

 ature, when the colonies will show a flat central nucleus, 

 transparent and bluish, surrounded by a prominent and 



Fig. 155. Culture of bacillus icteroides on agar (Muir and Ritchie). 



opaque zone, the whole resembling a drop of sealing-wax. 

 Sanarelli refers to this appearance as constituting the chief 

 diagnostic feature of Bacillus icteroides. It can be observed 

 in twenty-four hours. 



Blood-serum. Upon blood-serum the growth is very 

 meager. 



